F5 Maths

圖片參考：http://img695.imageshack.us/img695/1302/81036391.png


Let O be the centre ,

OA = OB = OC = OD
AB = BC = CD

△OAB =~= △OBC =~= △OCD (S.S.S.)

ㄥAOB = ㄥBOC = ㄥCOD = 60° since the sum of them = 180° .

y = ㄥABO + ㄥCBO = (180 - 60)/2 + (180 - 60)/2 = 120°
Simiular ㄥBCD = 120°

So ㄥDAO + ㄥCDO = 360 - 120 - 120 = 120°

Since AD is diameter , ㄥAED = 90° so ㄥOAE + ㄥODE = 180 - 90 = 90°

The answer = y + ㄥDAO+ㄥCDO + ㄥOAE+ㄥODE = 120 + 120 + 90 =

330°

(C)